Wound dressing containing a vacuum pump

ABSTRACT

The present invention relates to a wound healing PVA sponge dressing using negative capillary pressure of the dressing material together with auxiliary negative pressure for wound treatment. The PVA sponge dressing is pretreated with gram positive and gram negative biocidal 5 dyes for insertion into or over a wound. A negative pressure pump is mounted to the PVA sponge dressing to produce additional capillary pressure for withdrawing fluid or water vapor from the sponge dressing and a cover is mounted over the sponge material and negative pressure pump forming a unitary sealed package for placement over a wound.

RELATED APPLICATIONS

This application is a continuation application of Application No.16/602,519, filed Oct. 24, 2019, which is a utility patent applicationclaiming priority and benefit from U.S. Provisional Pat. Application No.62/749,902 filed Oct. 24, 2018, the contents of which in their entiretyare herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None

REFERENCE TO SEQUENCE LISTING, A TABLE OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

None.

BACKGROUND OF THE INVENTION 1. Field of Invention

The present invention is directed toward a PVA wound dressing for thetreatment of wounds containing a pump which administers negativepressure to the wound site.

2. Background of the Invention

Negative pressure wound therapy (NPWT) has long been used in thetreatment of wounds and improves the rate of wound healing whileremoving fluid, exudates, bacteria and other healing inhibitingsubstances from the wound site. Extensive studies of both continuous andintermittent treatment of wounds under negative pressure were conductedin the 1980′s and 1990′s in various Russian institutions. This testingdemonstrated that slow healing wounds healed substantially faster withnegative pressure. It was also shown that treatment of wounds withnegative pressure produced an antibacterial effect. These studies aredescribed in articles in the Russian medical journal Vestnik Khirurgil.It is believed that such negative pressure wound therapy hastens woundclosure by speeding migration of epithelial and subcutaneous tissueadjacent the wound towards the center and away from the base of thewound until the wound closes.

Negative pressure therapy also known as suction or vacuum therapy hasbeen used in treating and healing wounds. Application of negativepressure, e.g. reduced or subatmospheric pressure (pressure below normalatmospheric pressure), to a localized reservoir over a wound has beenfound to assist in closing the wound by promoting blood flow to thearea, stimulating the formation of granulation tissue, and encouragingthe migration of healthy tissue over the wound. This technique hasproven particularly effective for chronic or healing-resistant wounds,and is also used for other purposes such as post-operative wound care.

Thus, it is known that negative pressure wound therapy assists in theclosure and healing of many forms of “hard to heal” wounds by reducingtissue edema, encouraging blood flow and granular tissue formation,and/or removing excess exudate and can reduce bacterial load (and thusinfection risk).

Generally, negative pressure therapy provides for a wound to be coveredto facilitate suction at the wound area. A conduit is introduced throughthe wound covering to provide fluid communication to an external vacuumsource. Atmospheric gas, wound exudates, or other fluids may thus bedrawn from the reservoir through the fluid conduit to stimulate healingof the wound. Exudates drawn from the reservoir may be deposited in acollection canister or container.

U.S. Pat. No. 3,572,340 issued Mar. 23, 1971 discloses a pump in theform of an elastically compressible body made of an open celled foammaterial, preferably polyurethane foam which body also serves as areceptacle for fluid drained from a wound. The pump is said to have acapacity to maintain a negative pressure of 15-80 mmHg for over 48hours. A drain placed in the wound pocket and is connected to the pumpby a tube.

See also U.S. Pat. No. 4,525,166 issued Jun. 25, 1985 which useslaminaria (kelp) instead of foam. Laminaria swells by absorption ofliquid and does not release the liquid.

U.S. Pat. No. 7,569,742 issued Aug. 4, 2009 discloses a wound dressingapparatus using a micro pump system housed within or above a wounddressing member. The micro-pump includes a miniature pump that applies asub-atmospheric pressure to the wound to draw wound fluid or exudateaway from the wound bed while allowing patient mobility.

U.S. Pat. No. 9,084,845 issued Jul. 21, 2015 discloses a number of pumpassemblies for reduced pressure wound therapy which are battery powered.The embodiments show a housing, a pump, a flow pathway through the pump,one or more valves in communication with the housing and a one waypressure sensor in communication with a fluid pathway.

In U.S. Pat. No. 9,974,890 issued May 22, 2018 discloses a portablesystem for sub-atmospheric pressure therapy in connection with healing asurgical wound, including a wound dressing dimensioned for positioningrelative to a wound bed of a subject and a sub-atmospheric pressuremechanism carried or worn by the subject. The sub-atmospheric pressuremechanism includes a housing having a control unit adapted to draw avacuum and a canister associated with the housing. The canister has acollection bag disposed therein, which is in fluid communication withthe wound dressing to receive exudates from the wound bed. Thecollection bag is adapted to expand upon receipt of the fluids andreleases gas with operation of the control unit.

U.S. Pat. No. 10,046,096 issued Aug. 14, 2018 discloses a number ofembodiments, some of which have a pump assembly mounted to or supportedby a dressing for reduced pressure wound therapy. The dressing can havevisual pressure, saturation, and/or temperature sensors to provide avisual indication of the level of pressure, saturation, and/ortemperature within the dressing. The pump assembly can have a controllersupported within or by the housing, the controller being configured tocontrol one or more operations of the pump. The pump is configured to besterilized.

U.S. Pat. Application Publication No. 2010/0324510 published Dec. 23,2010 disclosed a number of embodiments for treating wounds with reducedpressure. The preferred device is a sealing film which covers the woundas well as a tube which connects a space over the wound and beneath thesealing film to the negative pressure source which is preferably a pump.An open foam hydrophilic material of polyurethane is cut to the shape ofthe wound to fill the wound pocket. See also U.S. Pat. ApplicationPublication No. 2011/0178451 published Jul. 21, 2011 which is directedto foam wound inserts having high density and low density regions whichare subjected to negative pressure.

Current negative pressure wound therapy (NPWT) systems are generallycomprised of a wound dressing, a canister to collect wound exudate, anda pump or a vacuum source. The SNAP system relies on a mechanical vacuumsource and a canister to collect exudate (see U.S. Pat. ApplicationPublication No. 2011/0230849 published Sep. 22, 2011), while the PICOsystem (see U.S. Pat. Application Publication No. 2010/0160881 publishedJun. 24, 2010) relies on an electrical vacuum source and uses thedressing to collect the exudate. In these cases, a therapeuticallyuseful reduced pressure (i.e. vacuum or negative pressure) is achievedthrough the vacuum source.

There are numerous problems with the current prior art. The vacuumsource is far from the wound bed, creating a need for tubing that isuncomfortable and unsightly for the patient, leading to complianceissues. Tubing can be crimped or clogged leading to failure. Insubfreezing climates, the tubing can freeze and as a result, clogleading to failure. The pump must reduce the pressure requiring largemechanical or electrical units that can be bulky and noisy. This isfurther exacerbated by long lengths of tubing that result in greaterpressure drop over distance, in turn requiring a larger and morepowerful pump. A separate wound dressing is used with the prior artnegative pressure pumps and the dressing itself is not actively used totreat the wound with natural capillary pressure or kill bacteria,prevent bacteria reproduction or inhibit or destroy biofilm formingwithin the wound.

SUMMARY OF THE INVENTION

The present invention describes a medical wound dressing device in thefield of wound care treatment and is comprised of a porous PVA spongematerial dressing having a natural capillary pressure. The device isalso provided with a biocide. The device is also provided with a sealingdrape covering the porous PVA sponge dressing material, an auxiliaryvacuum generator mechanism such as a negative pressure pump connected tothem porous PVA sponge dressing material and a fluid removal path withan optional fluid return path back to the dressing. The device enablesthe application of negative pressure to the porous PVA dressing materialand the adjacent wound while covering the wound.

It is an object of the invention to provide a constant source of lownegative pressure on the wound through the natural capillary pressure ofthe porous sponge dressing material while systematically providing asecond higher negative pressure on the wound by applying a secondarynegative pressure.

It is another object of the invention to provide a natural capillarypressure wound dressing material to a wound and applying additionalnegative pressure to the dressing material and wound by a vacuummechanism which heals and closes a wound in quicker time thanconventional wound dressings.

It is still another object of the invention to provide a wound dressingmaterial having a natural capillary pressure and providing additionalmechanical negative pressure to the dressing material which is superiorto only mechanically produced negative pressure application to a wound.

It is another object of the invention to provide a wound dressing devicewhich is disposable;

-   It is yet another object of the invention to provide a wound    dressing device which is easier to apply to the user;-   It is another object of the invention to provide a continuous    operational status to the user and alert the user of any operational    problem with the device with visual and tactile indicators; and-   It is still another object of the invention to provide a    self-contained wound dressing device that can be easily carried by    the patient being treated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to the appendedFigures, in which:

FIG. 1 is a schematic cross section of the inventive negative pressurewound dressing device;

FIG. 2 is a schematic cross section of another embodiment of thenegative pressure wound dressing device;

FIG. 3 is a schematic of the negative pressure provided to the wounddressing of FIGS. 1 and 2 using the inventive wound dressing device; and

FIG. 4 is a schematic of a detailed control circuit of the inventivewound dressing device.

These and other objects, advantages, and novel features of the presentinvention will become apparent when considered with the teachingscontained in the detailed disclosure along with the accompanyingdrawings.

DESCRIPTION OF THE INVENTION

The present invention is a negative pressure wound therapy (NPWT) systemwhere the reduced atmospheric pressure on the wound is achieved by twosources, (1) a porous sponge dressing material and (2) an auxiliaryvacuum unit, e.g. a pump. The porous sponge dressing material is a PVAfoam which provides a natural capillary pressure of about -20 mmHg toabout -72 mmHg on the wound. The auxiliary pump can further reduce thepressure to maintain a therapeutic benefit, e.g. down to about -120mmHg. The result is a NPWT system that is portable by the user and issignificantly smaller than prior art devices and with minimal to notubing required to connect the dressing to the auxiliary vacuum source.

As is used herein, reduced or negative pressure levels, such as -X mmHg,represent pressure levels relative to normal ambient atmosphericpressure, which corresponds to 760 mmHg (or 1 atm, 29.93 inHg, 101.325kPa, 14.696 psi, etc.). Accordingly, a negative pressure value of -XmmHg reflects absolute pressure that is X mmHg below normal ambientatmosphere pressure of 760 mmHg or, in other words, an absolute pressureof (760 mmHg -X mmHg). In addition, negative pressure that is “less” or“smaller” than the X mmHg negative pressure corresponds to pressure thatis closer to atmospheric pressure.

The present invention describes a medical dressing device for the fieldof wound care of patients and is comprised of a porous sponge dressingmaterial 10, preferably PVA foam sponge material 12, a sealing drape orcover 20, a fluid removal path 30, and a vacuum producing mechanism 40as seen in FIGS. 2 and 4 . The device enables the application ofnegative pressure to a wound with absorption of fluid to the poroussponge dressing material.

The porous sponge dressing material of the invention is preferably PVAfoam sponge material 12 and acts as a source for negative pressurethrough its natural capillary action and as a wound exudate collectionvehicle. The term PVA foam refers to one or more of the following:Polyvinyl formal, Polyvinyl acetal, PVA copolymers of vinyl esters andPVA copolymers of ethylene-containing repeat units. Copolymers with PVAmay be random, block, alternating, periodic or graft. The acetal groupmay have one or two substituents such as aliphatic or aromatic groupswhich may be further substituted. Foams may further be comprised ofblends of above PVA based polymers with non-PVA polymers. The porous PVAsponge 12 has a surface chemistry and porosity that create capillaryflow properties, which in turn provide for a natural capillary pressureleading to exudate being drawn from the wound into the porous material.The reduced pressure created by the capillary action of the porousmaterial enables the auxiliary vacuum unit or vacuum producing mechanism40 as shown in FIGS. 1 and 2 to do less work, thereby affording smallerand less energy consuming technologies to be employed over currentcommercial products.

While the porous sponge dressing material is generally referred to bythe numeral 10 and the PVA sponge dressing material is referred to bythe numeral 12, these numbers can be interchanged as necessary as bothrefer to the sponge dressing material.

The PVA porous dressing material 12 acts as a dressing to the woundsurface 14. This material is polymeric in composition where the polymercan be a synthetic substance, a natural substance or combinationsthereof. In the preferred embodiment, the polymer is foamed PVA withpositive and negative biocidal dyes which impregnate or bind to thesponge receptor sites. The porous PVA sponge dressing material has amorphology characterized by an average pore throat diameter of 10 - 500pm, a fluid retention of 5.5 - 300 mL fluids/g porous material, adensity of 0.05 - 0.15 g polymer/cm3 porous material, and a porosity of60 - 99.5%. The cell structure is characterized as open / interconnectedwith through pores that can be evaluated by techniques such as capillaryflow porometry and liquid extrusion porosimetry. The natural capillarypressure of the PVA sponge or foam dressing material ranges from about-20 mmHg to about -70 mmHg. This natural capillary pressure ranges andfalls within the low to mid-range settings of presently used mechanicalvacuum machines.

Without wishing to be bound by theory, the porous PVA sponge dressingmaterial has one or more material properties which in combination affordfluid flow through the material to create a natural capillary pressure.Material properties may include the pore properties above, surfacechemical structure, surface roughness and the resultant interfacialtensions arising from the porous PVA material surface and the fluidsurface in contact with other. Porous PVA materials with naturalcapillary pressure may be differentiated from porous materials withoutnatural capillary flow by their simplified diffusion coefficient (D)which can be calculated from the general form of the Washbum equation:

$\text{D=}\frac{\text{L}^{2}}{\text{t}}$

where (L) is the wicking distance of the liquid at time (t).

In a preferred embodiment the porous PVA sponge dressing material havingnatural capillary pressure has a simplified diffusion coefficientgreater than 0.3 cm² 1 second; in a more preferred embodiment greaterthan 0.4 cm² / second, and in a most preferred embodiment greater than0.5 cm² / second. As shown in Table 1, dressings used in the field todayhave little to no natural capillary pressure as measured by theirsimplified diffusion coefficient whereas the porous PVA foam of thepresent invention surprisingly has an almost 4-5X ability.

TABLE 1 Negative Pressure Wound Therapy Dressing Negative DiffusionCoefficient (W/s) KCISNAP Dressing 0.00 KCIVAC Whiteman 0.00 CorkMedical NPWT Black Foam 0.00 Cardinal Health NPWT Black Foam 0.00 GelTexNFWI Dressing 0.00 DeRoyal Top Draw Black 0.00 Porous PVA Foam 0.98

The simplified diffusion coefficient may be determined to suspending aswatch of the dressing (0.5” × 0.25” × 3.0”) in a normal saline solutionto allow vertical wicking through the dressing material. Prior toevaluation, all materials are conditioned at ambient temperature for atleast 24 hours. The test article is then attached to a suspensionfixture and lowered into a test beaker containing saline solution suchthat one end is slightly submerged in the saline solution. The verticalwicking distance is recorded after 45 seconds. This wicking distance isthen corrected to account for the initial height of saline, and thediffusion coefficient is calculated from the corrected wicking distanceand wicking time period.

A biofilm enzymatic solution can also be incorporated into the poroussponge dressing material during the same manufacturing process thatbinds the antibacterial agents but after addition of the antibacterialagents. During this process, Methylene Blue, Crystal Violet, and biofilmprevention enzyme solution is introduced and allowed to uniformlyimpregnate or bind to the foam matrix. The product is then dried andprocessed to final specification and sterilization.

The porous sponge dressing material may further have agents that bindand/or eliminate toxins from the exudate, e.g. bacteria, mold, spores,endotoxins. The present invention uses foamed polyvinyl alcohol which istreated to open up the binding sites of the foam. The washed foam issoaked with one or more gram positive dyes selected from a group of dyesconsisting of Gentian Violet dye, also called Crystal Violet dye,Malachite Green dye, Brilliant Green dye, Quinacrine dye and Acriflavindye and one or more gram negative dyes selected from a group of dyesconsisting of Methylene Blue dye, Dimethyl Methylene Blue dye, NewMethylene Blue dye. The preferred dyes used in the invention areMethylene Blue dye and Gentian or Crystal Violet dye are attached to afinite number of the binding sites in the foam. Generally,electronegative (acidic) dyes are more effective on Gram-negativebacteria and electropositive (basic) dyes are more effective on Grampositive bacteria such as Staphyloccus aureus.

The porous sponge dressing material may be shaped if desired to beconformable to the shape of the wound bed. The porous sponge dressingmaterial may have a surface porosity on the surface distal to the woundthat allows for moisture transmission outwards but is impermeable to air(inwards). As a result, the porous sponge dressing material canself-rejuvenate until it is fully loaded with exudate, up to 5x, 10x oreven 15x its weight in exudate fluid, at which time the dressing wouldbe replaced.

This sponge material of the invention may further be combined withclinically safe agents, e.g. saline, hydration fluids, antimicrobialagents, softening agents, stiffening agents, or wetting agents. Theagents may be preloaded prior to clinical use or may be loaded by aclinician at the time of clinical use.

In another example, the synthetic polymer can be polyvinyl formal. Thenatural polymer material can be either animal or plant derived, forexample, collagen, chitosan, or polyethylene terephthalate.

The sealing layer, drape or cover 20 acts to form a vacuum seal over thedressing 12 to the wound perimeter. The sealing layer 20 may bepolymeric in composition where the polymer can be a synthetic substance,a natural substance or combinations thereof. The sealing layer may alsobe metallic in composition. The sealing layer may be comprised ofmultiple polymeric and or metallic layers and may further have adhesiveson its surfaces or between layers.

The vacuum connection assembly 30 acts to apply auxiliary vacuum throughthe sealing layer 20 to the sponge dressing 12 from the vacuum mechanism40 via plastic conduits 82 and 80 as seen in FIG. 4 , or nipples 42 asseen in FIG. 2 , or nipple 30 as seen in FIG. 1 . The fluid removalassembly (conduit, T-section, nipples) may be polymeric in compositionwhere the polymer can be a synthetic substance, a natural substance orcombinations thereof. The vacuum connection assembly may also bemetallic in composition or a combination of polymer and metal. Thevacuum connection path may be affixed external to the sealing layer orbe imbedded within the sealing layer.

The vacuum mechanism 40 provides a clinically beneficial negativepressure (up to -120 mm Hg) to the wound site 14 through the porous foamdressing material 10/12. The vacuum mechanism 40 may be affixed externalto the sealing layer 20, positioned adjacent the sealing layer or beimbedded within the sealing layer and draws fluid away from the porousfoam sponge material through one or more paths. The vacuum or negativepressure is achieved and controlled through many methods known to thoseskilled in the art. In one embodiment, the vacuum is achieved through anenergized device. In another embodiment, the vacuum is achieved througha manual process such as a syringe or squeeze bulb. Preferably, thedevice is a mechanical pump which is energized or powered by batteries.The vacuum mechanism may allow for filtration of fluid prior to enteringthe fluid return path. The vacuum mechanism may allow for the additionof clinically safe agents to the fluid prior to entering the fluidreturn path.

The medical device described in this invention may be single use andthus disposable or one or more of its components may be reusable. It isenvisioned that all components will be disposable and that a whole unitwill be disposable as medical waste. The device may be fully assembledwhen received by the customer or may require assembly at the point ofcare.

The NPWT system of the invention may optionally have a sealing layer 20as shown in FIG. 2 on the porous material surface 10 that allows forvapor or moisture transmission outwards but is impermeable to air(inwards). In other words, the layer 20 is both vapor permeable and anair barrier. As noted above, this would enable the porous spongematerial to self-rejuvenate until it is fully loaded with exudate. Inone embodiment, the sealing layer covers only the distal facing poroussponge material surface and abuts the auxiliary vacuum unit. In anotherembodiment, the sealing layer extends over the auxiliary vacuum unit,and the vacuum exhaust passes through the sealing layer. In yet anotherembodiment, the sealing layer runs under the auxiliary vacuum unit andthe vacuum auxiliary units sits above the sealing layer. In a preferredembodiment, the sealing layer is translucent to aid in visualization ofthe porous sponge material by the clinician or patient.

As previously noted, the inventive assembly may have a vacuum connectioncomponent 30. This component would be located between the auxiliaryvacuum unit 40 and the foamed porous material dressing 10/12. In oneembodiment of the invention, the vacuum connection component has bafflesor channels that aid in equilibrating the vacuum from the auxiliaryvacuum unit 40 to the porous material 10/12 or aid in distributingfiltered exudate back to the porous material. One or a plurality offluid removal and/or fluid return chambers may be used where eachchamber has one or more of the functions listed above.

The vacuum connection component may also be provided with a vacuumport/valve. This port/valve component is gas permeable but not liquidpermeable and acts to protect the auxiliary vacuum unit from beingfouled by exudate. In another embodiment, the assembly may be providedwith a check valve to prevent back flow of air into the vacuumconnection component and/or the porous sponge material. In yet anotherembodiment, the vacuum connection component may have a length of tubingto separate the auxiliary vacuum unit from the porous sponge material.One or a plurality of vacuum port/valves may be used where each unit hasone or more of the functions listed above.

The auxiliary vacuum unit 40 of the invention (see vacuum motor 78 inFIG. 4 ) supplements the negative pressure provided by the foam porousdressing material 12 so that the total negative pressure on the woundremains in a clinically beneficial range. In one example (FIG. 3 ), theporous material 12 alone provides negative pressure that is above theclinically beneficial threshold, and the auxiliary unit supplements thatpressure by raising the pressure higher in the therapeutic range. Asexudate is drawn into the foam porous dressing material 12, air ormoisture exhaust from the system and/or leaks occur in the system, thepump can apply vacuum to maintain the therapeutic range. As the porousmaterial gets filled, its contribution to maintenance of thetherapeutically beneficial negative pressure decreases and the auxiliaryvacuum unit’s contribution increases. When the porous material is fullysaturated, and/or the auxiliary vacuum no longer has power sufficient tohold a therapeutic negative pressure, the NPWT system can be replacedwith a new device. It should be recognized that the system’s designallows for different ratios of negative pressure contribution from theporous material and auxiliary vacuum unit, and that the ratio may varyover the course of the treatment period.

As previously noted, the auxiliary vacuum unit can be powered by amechanical action, e.g. a syringe force. The auxiliary vacuum unit(pump) is preferably powered with an electrical supply, most preferablya battery. Examples of battery powered pumps that could be used in theauxiliary vacuum unit include Models Compact/OEM and KPV-14A availablefrom Cole Parmer, Model NMP 03 KP DC-S available from KNF Neuberger,Inc. and Model SX-1 from Binaca Products.

While the auxiliary vacuum unit 40 can sit on the distal (outward)facing surface of the porous material 10/12, the auxiliary vacuum unit40 can be embedded or encased in the porous material 10/12 to provide alow-profile system.

The auxiliary vacuum unit 40 may have addition features including:

-   Pressure feedback loop enabling constant pressure adjustment-   Pressure feedback loop enabling intermittent pressure adjustment    (cycling)-   Pressure cut off detection when pressure is beyond therapeutic level-   Leak detection when pressure decay is too rapid-   Pressure ramp up detection when rate (mm Hg/sec) of pressure    increase is too steep, indicating the porous material or fluid    removal/fluid return chamber is saturated or exhausted-   Total pressure reduction in a cycle, which when above a threshold,    indicates the porous material or fluid removal/fluid return chamber    is saturated or exhausted

The auxiliary vacuum unit 40 is provided with an integral motor 78 andcan also be provided with a vacuum exhaust component that allows escapeof air and moisture vapor that has traveled through the auxiliary vacuumunit. The vacuum exhaust component may sit on the surface of theauxiliary vacuum unit or be attached to the auxiliary vacuum unitthrough a length of tubing. One or a plurality of vacuum exhausts may beused. The auxiliary vacuum unit may also serve as a check valve toprevent back flow of air into the auxiliary vacuum unit.

The NPWT system may further have a sealing drape layer 20. The sealingdrape layer 20 acts to seal the wound bed in an airtight manner. It canalso act as the moisture vapor transmission layer described above. Inthis case, the sealing layer may cover the auxiliary vacuum unit, porousmaterial and other components of the device. In another modification,the sealing drape layer is non-permeable. In this case it would run fromthe healthy skin to the moisture vapor transmission layer, or it wouldstill cover the entire NPWT system where moisture transmission would bethrough the auxiliary vacuum unit or vacuum exhaust component.

The overall system is a single use, disposable product. The system issupplied sterile and have a useful lifetime of approximately 1 day, morepreferably 2-3 days, and most preferably up to 7 days depending upon thetype and severity of the wound.

The control system 70 as schematically shown in FIG. 4 comprises a lowpower microcontroller 71, a three LED indicators 72, one or more pushbutton switches 74, ambient 76 a and vacuum 76 b pressure sensors, avacuum motor 78, motor power control 79, one or more batteries 77 and atactile feedback device 72 a. The vacuum pressure sensor has a “T”attachment 82 connecting it to the plastic conduit 80 (for vacuumconnection component 30) which connects the vacuum motor to the wounddressing 10 placed on the patient wound 14. The ambient pressure sensor76 a is open to the atmosphere. The microcontroller implements the logicdescribed herein with the C source code language compiled and downloadedfor execution to the microcontroller.

The clinically therapeutic negative pressure range for the device isabout -60 mmHg to about -120 mmHg which is shown in FIG. 3 by the letterR. A normal working cycle is shown in FIG. 3 . The ramp up is shown bythe letter A and the decay is shown by the letter D. However, it ispreferred that the negative pressure should fall within about -80 mmHgto about -100 mmHg and most preferably about -85 mmHg to about -95 mmHg.

The negative pressure cut-off value for the device is about -120 mmHg.Beyond this value, the patient experiences discomfort.

The push button and three LED’s provide the device user interface. Whenthe push button is first pushed, the device starts up, performs aninitial operational check and indicates it is ready for operation byilluminating a green LED. The second time the push button is pushed, thedevice initiates treatment and starts monitoring operational status.Good status is indicated by an illuminated green light. Warning statusis indicated by an illuminated yellow light and a unique tactilefeedback pattern. Error status is indicated by an illuminated red lightand a different unique tactile feedback pattern.

Having separate ambient and vacuum absolute pressure sensors haveadvantages over a single differential sensor common the state of theart. Differential pressure sensors require that the path to the ambientpressure be physically adjacent to the path to the vacuum pressure.Separate sensors allow the paths to be physically separated.Differential pressure sensors are bulky and difficult to mount, whereasabsolute pressure sensors are small with a wide variety at mountingoptions. The ambient pressure sensor provides barometric pressure, whichcan provide an input to the volume calculations to determine theoperational status.

At the onset of treatment with the dressing properly secured with noleaks, the device undergoes initial start-up. The vacuum motor 78 willturn on and remain running until it reaches the upper therapy threshold,at which point the vacuum motor is turned off and the pressure controlwill start.

Pressure control consists of reading the ambient and vacuum pressuresensors periodically. Each time a sensor is read, the vacuum level iscalculated as the difference between the ambient and vacuum pressuresensors. If the vacuum is at or below the lower therapy threshold, thevacuum motor is turned on. When the vacuum subsequently reaches theupper therapy threshold, the vacuum motor is turned off.

Research has shown that a variable vacuum level may provide moreeffective therapy than a constant vacuum level. During the course oftherapy, the microcontroller may optionally change the upper and lowerthreshold values in a redetermined pattern over the course of severalminutes to improve the therapy effectiveness. In another embodiment, thepressure is held constant.

Operational status monitoring will run continuously once the NPWT deviceis started with the first push of the button. The status monitoring willinclude battery level, leak detection, microcontroller health, blockagedetection, loss of volume capacity and device lifetime. The batterylevel will be monitored using both coulomb counting methods, and voltagelevel measurements. A warning level and error level will be establishedfor battery monitoring based on battery characteristics. Leak rate willbe calculated by summing the time of the ramp up (A in FIG. 3 ) over aknown time combined with the vacuum pump characteristics. The warninglevel will be established based on a projection of the loss of 20% ofthe lifetime of the device. The error level will be the point where thedevice is no longer able to maintain the pressure above the lowertherapy threshold or the projected lifetime of the device due to theleak is less than 12 hours. The microcontroller health will be monitoredby a hardware watchdog, which will turn off the device if themicrocontroller does not run the pressure control logic at the selectedperiodic rate. The microprocessor will track the elapsed time that theNPWT has provided therapy. When the elapsed time is within 12 hours of apredetermined lifetime, the device will shut down the therapy, and turnoff all the indicator LED’s.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.However, the invention should not be construed as limited to theparticular embodiments which have been described above. Instead, theembodiments described here should be regarded as illustrative ratherthan restrictive. Variations and changes may be made by others withoutdeparting from the scope of the present invention as defined by thefollowing claims:

What is claimed is:
 1. A method for wound treatment comprising: applyingnegative pressure to a wound using a porous material having a naturalcapillary pressure; supplementing the negative pressure applied by theporous material using a negative pressure pump connected to the porousmaterial by turning the pump on; turning the pump off; and turning thepump on again.
 2. The method of claim 1, wherein supplementing thenegative pressure using the pump comprises applying supplementalnegative pressure so that a total negative pressure on the wound remainsin a therapeutic range.
 3. The method of claim 1, wherein: applyingnegative pressure to the wound using the porous material comprisesapplying negative pressure that is above a lower therapy threshold; andsupplementing the negative pressure using the pump comprises raising alevel of pressure on the wound higher in a therapeutic range.
 4. Themethod of claim 1, wherein supplementing the negative pressure using thepump comprises increasing negative pressure applied by the pump.
 5. Themethod of claim 1, further comprising replacing the porous material whenthe porous material is fully saturated.
 6. The method of claim 1,further comprising replacing the porous material when the pump no longerhas power sufficient to hold a predetermined level of pressure on thewound.
 7. The method of claim 1, comprising varying a ratio of negativepressure contribution from the porous material and pump during the woundtreatment.
 8. The method of claim 1, further comprising adjustingnegative pressure applied by the pump.
 9. The method of claim 1, furthercomprising: detecting when a level of pressure on the wound is outsideof a therapeutic range; and turning the pump off when the level ofpressure on the wound is above an upper therapy threshold.
 10. Themethod of claim 1, further comprising detecting decay of a level ofpressure on the wound.
 11. The method of claim 1, further comprisingdetecting a rate of increase of a level of pressure on the wound. 12.The method of claim 1, wherein the porous material comprises polyvinylformal, polyvinyl acetal, polyvinyl acetal copolymers of vinyl esters,polyvinyl acetal copolymers of ethylene-containing repeat units, or acombination thereof.
 13. The method of claim 1, wherein the porousmaterial comprises polyvinyl formal, polyvinyl acetal.
 14. The method ofclaim 1, further comprising calculating a level of pressure on the woundbased on ambient pressure and vacuum in the porous material.
 15. Themethod of claim 14, comprising turning the pump on again if the level ofpressure on the wound is at or below a lower predetermined level. 16.The method of claim 15, further comprising turning the pump off againwhen the level of pressure on the wound subsequently reaches an upperpredetermined level.
 17. The method of claim 16, further comprisingmeasuring total pressure reduction in a cycle.
 18. The method of claim1, further comprising monitoring battery level, leak detection,microcontroller health, blockage detection, loss of volume capacity,device lifetime, or a combination thereof of a wound negative pressurewound therapy device comprising the porous material and the pump. 19.The method of claim 18, further comprising indicating a warning orshutting down the device when the device is no longer able to maintainpressure above a lower therapy threshold.
 20. The method of claim 18,further comprising: tracking elapsed time that the device has providedtreatment; and indicating a warning or shutting down the device based onthe elapsed time.